Integrated circuit design specifications generally include limits for the transition times and slew rates of output signals. For example, recent Mobile Industry Processor Interface (MIPI) input/output (I/O) interface standards, such as Serial Low-power Inter-chip Media Bus (SLIMBus), have called for limited output slew rates across a very wide range of output loads (e.g., 15 pF-75 pF) and across process, voltage and temperature (PVT) variations. Such standards also call for multiple output voltage modes.
Variations in the load capacitance coupled to output circuitry on an integrated circuit chip affect the slew rates and transition times of the output signals. Output interface circuitry on a chip may include capacitive feedback, which compensates for some variations in load capacitance but may not be capable of meeting tight transition time specifications. For interfaces that are designed to provide a limited output slew rate across a very wide range of output capacitive loads, general purpose input/output (GPIO) circuitry may not be able to provide output signals that satisfy the transition time requirements, even if such circuitry includes output drivers with capacitive feedback.
Because of the continued rapid scaling of complementary metal oxide semiconductor (CMOS) technology, the use of off-chip components is becoming more expensive. Compensation techniques that involve off-chip calibration are therefore increasingly expensive to implement. Thus, the use of off-chip components is generally limited to applications that rely on highly accurate delay calibration. Even presently known off-chip calibration techniques may not be effective to compensate for very wide variations in output load capacitance.